The disclosed invention is directed generally to hybrid multilayer circuit structures, and is directed more particularly to connected microstrip transmission lines of different dimensions disposed on hybrid multilayer circuit structures and having a substantially constant impedance.
Hybrid multilayer circuit structures, also known as hybrid microcircuits, implement the interconnection and packaging of circuit devices (e.g., integrated circuits), and generally include a unitized multilayer circuit structure formed from a plurality of integrally fused insulating layers (e.g., ceramic layers) having conductor traces disposed therebetween. The circuit devices are commonly mounted on the top insulating layer so as not to be covered by another insulating layer or on an insulating layer having die cutouts formed thereon to provide cavities for the circuit devices. Passive components such as capacitors and resistors can be formed on the same layer that supports the circuit devices, for example, by thick film processes, or they can be formed between the insulating layers, for example, also by thick film processes. Electrical interconnection of the conductors and components on the different layers is achieved with vias or holes appropriately located and formed in the insulating layers and filled with conductive via fill material, whereby the conductive material is in contact with predetermined conductive traces between the layers that extend over or under the vias.
Hybrid multilayer circuit structures are now being utilized for RF applications wherein microwave integrated circuits (MICs) and/or monolithic microwave integrated circuits (MMICs) mounted on a hybrid are interconnected by microstrip transmission structures formed on the multilayer structure, for example pursuant to screen printing or metal deposition.
A consideration with implementing microstrip transmission structures in hybrid multilayer circuit structures is the desirability of reducing signal reflection at the transitions between microstrip lines of different widths, where a variable width is being utilized for considerations such as reducing loss, layout requirements and processing requirements.